1. Field of the Invention
The present invention relates generally to a semiconductor laser array including a sequence of laser active strips disposed adjacent one another.
2. Description of the Related Art
To achieve high intensity laser emissions from a semiconductor laser or laser diode, it is known to arrange semiconductor laser diodes in an array. Such an array is composed of a plurality of laser diodes disposed parallel next to one anther lying in a semiconductor body. Each and every one of the laser diodes is in the form of a laser active strip in the semiconductor body. Given a tightly adjacent arrangement of laser active strips, wave mechanical, or wave optical, coupling of the individual laser active strips relative to one another results so that the individual laser active strips emit mutually coherent radiation. In other words, the total emission output of the laser array is coherent in and of itself.
The neighboring laser active strips of an array exhibit lateral coupling which has a tendency to excite a coupled oscillation mode so that part or all of the neighboring strips oscillate in a phase respectively shifted by 180.degree. relative to one another. The individual laser active strips in fact emit coherent radiation, but this radiation has an opposite phase at the exit location on the end face of the semiconductor diode from one strip to the next. Two emission lobes, thus, derive as a result of the interference and, more or less noticeable subsidiary lobes occur dependent on the number of interfering strips. Such mutual coupling of the strips reduces the usability of such an array to a rather considerable degree.
Semiconductor laser arrays are known from Appl. Phys. Lett., vol. 42 (1983) pages 554-556; U.S. Pat. No. 4,217,561; U.S. Pat. No. 4,509,173; and from Elec. Lett., vol. 21 (1985) pages 347-349.
The aforementioned publications and the U.S. Pat. No. 4,509,173 specify measures with which phase-coupled radiation emissions are achieved in a laser array. To this end, measures are undertaken to provide branching and rejoining of the raditional paths of the generated laser emission in the laser active layer of the semiconductor body. Such arrangements necessarily have nonparallel path portions for guidance of the laser radiation. Technological difficulties arise, particularly for such arrangements which are in the form of MCRW lasers.
A metal clad ridge waveguide laser is disclosed in U.S. Pat. No. 4,352,187, in which mutual energy exchange of laser active strips is recognized.